Behavioral, physiological and anatomical studies will be carried out on Pteronotus p. parnellii. These bats lend themselves well to the study of mechanisms controlling auditory input and they provide a model system for studies on acoustic-laryngeal interactions and morphological specializations of the cochlea for sharp tuning. Behavioral and physiological experiments will utilize simulated (pendulum) flight with animals actively involved in the echolocation of fixed, moving or fluttering targets. The responses of the cochlea, VIIIth nerve and CNS auditory centers to emitted pulses and echoes, and to CF and FM tone bursts will be monitored continuously during flight and a video system will record the animal's attentiveness to specific targets. Single unit studies will focus on the properties of auditory nerve fibers and on factors which affect sharp tuning. Special attention will be given to the labeling of cell populations with known frequency responses and the subsequent establishment of more precise cochlear frequency maps. Frequency maps will be superimposed on three-dimensional, computer reconstructions of the cochlea, VIIIth nerve and specific parts of the organ of Corti. The density, arrangement and physiological influence of a newly discovered layer of cells containing contractile proteins will be studied by immunocytochemical and electronmicroscopic techniques. The hypothesis that these cells contact and apply radial tension to the basilar membrane-spiral ligament complex and affect the mechanical properties of the cochlea will be tested. The physiological effects of the uptake and transport of latex microspheres by the VIIIth nerve will be analyzed and selective photothermolytic destruction of spiral ganglion cells and efferent cell bodies will be attempted. These studies have wide applications in the study of basic auditory mechanisms, in the development of more sophisticated active sonar systems for the blind, and in the potential application of photothermolytic techniques to the treatment of tinnitus or any disorder where selected groups of neurons might be advantageously destroyed.